var winWidth = 0;
var winHeight = 0;
function findDimensions() //函数：获取尺寸
{
//获取窗口宽度
if (window.innerWidth){
	winWidth = window.innerWidth;
} else if((document.body) && (document.body.clientWidth)){
	winWidth = document.body.clientWidth;
} 
//获取窗口高度
if (window.innerHeight){
	winHeight = window.innerHeight;
}else if ((document.body) && (document.body.clientHeight)){
	winHeight = document.body.clientHeight;
}

//通过深入Document内部对body进行检测，获取窗口大小
if (document.documentElement && document.documentElement.clientHeight && document.documentElement.clientWidth)
{
	winHeight = document.documentElement.clientHeight;
	winWidth = document.documentElement.clientWidth;
}
document.getElementById("bgimage").style.width = winWidth + "px";
document.getElementById("bgimage").style.height = winHeight + "px";
}
findDimensions();
//调用函数，获取数值
window.onresize=findDimensions;